1. Field of the Invention
This invention relates to a fibrous mat having good elasticity. More particularly, it relates to a fibrous mat which is substantially resistant to structural deformation upon repeated elongation, thus excellent in elasticity and fiber entanglement, highly flexible, rich in fullness, and firm-bodied, hence suited for use as a substrate for leather-like sheet materials.
2. Description of the Prior Art
Highly elastic fibrous mats have heretofore been prepared, for instance, by depositing short polyurethane fibers prepared by flush spinning (a method of producing fibers by taking advantage of the phenomenon of roping upon blowing off a molten polymer with high-speed air), followed by adhesion at the points of contact by self-agglutination or some other appropriate method, or by producing a polyurethane long fiber mat by the spun bond technique, such as disclosed in Japanese patent application Kokai No. Sho-52-81,177. With these polyurethane mats, however, it is difficult to attain a sufficient degree of fiber entanglement by conventional methods such as needle punching or entanglement by a high energy liquid stream, since the fiber itself is highly elastic and excessively flexible. It is thus impossible to prepare, by such conventional methods, a fibrous mat suited for use as a substrate for artificial leather, namely a fibrous mat having sufficient strength, a feeling indicative of firmness, and good elasticity or stretchability, and sufficient degree of fiber entanglement.
In Japanese patent application Kokai No. Sho-48-18,579, for instance, there is disclosed, as a fibrous mat having elasticity and strength, a fibrous mat produced by blending 5-80 weight percent of an elastic fiber with a nonelastic fiber. Since the elastic fiber and nonelastic fiber are significantly different in stiffness and elasticity, however, it is very difficult to attain sufficient blending of such fibers, or obtain a desired web on a card machine, or achieve a sufficient extent of entanglement. In fact, according to the above disclosure, such fibrous mat is produced by dispersing an elastic fiber and a nonelastic fiber in water and forming a mat on a screen in a manner of paper making, followed by simply bonding with a binder resin. Therefore, the fibrous mat obtained by the above method is not a three-dimensionally entangled fibrous mat, so that it is inferior or unsatisfactory in resistance to repeated deformation, in fullness, and in firm-bodiedness.
In Japanese patent application Kokai No. Sho-52-85,575, there is disclosed a method comprising making an entangled fibrous mat using a composite fiber made of a nonelastic polymer and an elastic polymer and then separating the component polymers from each other. However, a structure capable of affording a sufficient degree of elasticity cannot be produced by this method since the elastic polymer and nonelastic polymer are constrained both in the same condition. In Japanese patent publication No. Sho-40-2,792, a further method is disclosed which comprises forming a blend of a mix-spun fiber made of an elastic polymer and a nonelastic polymer with a mix-spun fiber made of nonelastic polymers into a fibrous mat, dissolving at least one of the nonelastic polymers in the fibers constituting the fibrous mat, and causing the nonelastic polymer to coagulate again within the fibrous mat. This method produces a fibrous mat having a sufficient extent of entanglement for use as a substrate for leather-like sheet materials. However, since the elasticity of this fibrous mat depends on the nonelastic polymer fiber, the mat exhibits insufficient elasticity. Thus, stretching of this mat by force will result in disengagement of entangled fibers from one another, leading to destruction of the mat structure. To sum up, the known methods to date have failed to provide an entangled fibrous mat which is satisfactory in both entangledness and elasticity.